This invention relates to countermeasures against infrared (IR) radiation-seeking devices and especially to a pulse system and method for jamming IR-seeking reticle-type missiles.
Present operational U.S. IR missile jammers rely on prior knowledge of threat-missile operating characteristics and, in fact, normally operate at frequencies close to those of threat-missile gyro spin rates. Previous IR countermeasures designed to defeat IR-guided missiles which use reticles for encoding target information utilize three general techniques: deception, disruption and damage. Deception and disruption generally occur at irradiance levels a few orders of magnitude greater than the seekers noise equivalent temperature (NET). This level may vary from 10xe2x88x9211 to 10xe2x88x928 watts/cm2 for most reticle-type seekers. Present jammers operate at jammer-to-target (J/S) signal levels of from 2 to 8, typically. Some jammers use electrically modulated, alkali-metal-seeded, rare-gas arc sources while some employ fuel-fired or electrically heated grey-body sources which are mechanically modulated by one or more rotating and/or slotted discs, slats or cylinders. The primary method of deception jamming employed these devices relies on the creation of false signals in the missile seekers electronic processing system, especially in the inner gyro tracking loop of spin-scan missiles. After amplification, this false or deceptive signal causes the gyro to precess in a direction looking away from the true target. The result when the target passes out of the gyro-telescope""s field-of-view is called xe2x80x9coptical break lockxe2x80x9d.
These jammers are also sometimes effective against conical-scan seekers but for somewhat different reasons. In con-scan seekers, the maximum disruption of the inner gyro tracking loop is usually no more than a wobble superimposed on the correct motion of the gyro as it follows the target. With deception jamming specially chosen frequencies pass into the seeker""s airframe guidance section which is disrupted by non-linearities, dither, or target-signal suppression. The end result for these con-scan seekers is that, although the gyro tracks, the canard wing deflections are either insufficient or too distorted to fly the missile to its target.
The primary disadvantage of present IR jammer systems is that their effectiveness depends on having prior information about the critical gyro spin frequencies of the threat missiles to be countered. Unfortunately, little is known about the internal functions of any but the oldest operational IR missiles in the inventories of various nations. There are additional difficulties, such as the spectral output and inflexibility of modulation schemes of current U.S. IR jammers.
Accordingly, an object of the present invention is to reduce the dependence of jam-format effectiveness against IR-seeker missiles on prior knowledge of threat-missile characteristics.
The objects and advantages of the present invention are accomplished by employing a pulse jamming system against IR-seeking missiles, in which the pulse-train characteristics, especially the pulse spacings, are randomized.